It won’t be perfect, you will loose a bit of oil, it shouldn’t be enough to matter but could be depending on how lucky you are. Put them on a vice upright, release the pressure, I remove the shrader valve. Unscrew the hose, install the elbow, connect the hose, keeping everything upright minimizing oil loss. Now to bleed it. With the hose fitting slightly loose add a very small amount of nitrogen (or argon if more readily available) until the air bubbles stop coming out, tighten the fitting. There may still be a bit of air but it will be very minimal. Recharge and install. Like I said not 100% perfect but close. The key is having the loose fitting at the high point when bleeding and doing it slow so the air escapes. There will be some fluid loss but I’ve had good success with this procedure.